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HUMBLE cotton could replace carbon nanotubes or metal threads in microfluidic analytical devices according to research reported in the American Chemical Society’s Applied Materials and Interfaces.

After treating generic cotton thread in a vacuum plasma reactor to remove its natural wax coating, researchers at Melbourne’s Monash University led by Wei Shen showed that liquids wick along the threads without the need for an external pump.

In a demonstration, cotton was stitched into a translucent polymer film in the pattern of the Olympic rings. The stitches of the threads pass one another from above and below the film without making contact so that different coloured inks wick along the threads without mixing.

“Threads allow complex continuous 3D microfluidic channels to be built without the need of patterned

barriers to define the liquid wicking passageways being tested, so complex channels and barriers do not need to be etched into the chip,” Shen and his colleagues report.

They also constructed sensors by sewing threads through a sandwich of polymer film and filter paper treated with indicators for the diagnostic biomarkers nitrite ion and uric acid. When the sensors were dosed with solutions of the targeted biomarkers, the filter paper changed colour within 5 seconds and showed increased colour intensity in response to stronger solutions.

They believe that cotton thread-based devices could have applications in developing countries where high-cost diagnostics are not available.

“Certain simple devices may even be fabricated by a skilled work force within the textile industry in developing regions,” the authors write. “It can be envisaged that thread, either alone or with other materials, can be used to fabricate a family of microfluidic diagnostic devices suitable for colorimetric, electrochemical, chemiluminescent, electrochemiluminesent assays and electrophoresis.”